Choke Out refers to intentionally cutting off oxygen to the brain for sexual arousal. Done alone, it's called autoerotic asphyxia. Other terms include asphyxiophilia or breath control play.
The choked person sometimes reports a feeling of euphoria, and heightened sexual arousal. For the dominant person, it's the ultimate control. Literally holding the other person's life in your hand.
During breathplay, the safest method available is to stop the submissive partner from breathing by covering the mouth and nose. That way you're not doing anything risky to the airway. Plus, you get the added benefit of watching them panic and struggle for air. When they begin to stop struggling, you can release the hold, and they should begin breathing again on their own.
WARNING: Choke out by squeezing the neck, throat, or arteries in the neck, can cause damage that might be permanent and/or fatal. Choking yourself out with rope, string, or a plastic bag, you might lose consciousness before you are able to release or remove the choking device.
In some Choke Out fatality cases, the body of the Choked Out individual is discovered naked or with genitalia in hand, with pornographic magazines nearby, with dildos or other sex toys present, or with evidence of having orgasmed prior to death.
David Carradine was found dead, curled up inside a closet with one end of a shoelace tied around his penis and the other end fastened around his neck.